1. Field of the Invention
The present invention relates to a camera with a lens barrel mechanism which is driven by a motor only in one rotational direction, wherein rotational power of the motor in the other direction is used for driving another mechanism.
2. Background Arts
An instant camera takes a photograph on a sheet of instant film by exposing the instant film to an optical image of a subject formed through a taking lens. After the exposure, a film feed out mechanism is driven to feed out the exposed instant film. The film feed out mechanism is constituted of a claw mechanism and a pair of developing rollers, and is driven by a motor. The claw mechanism rakes the exposed instant film out of a film pack loaded in the instant camera and feeds it toward the developing rollers. Then, the developing rollers nip and feed out the instant film through a film exit of the instant camera. While the instant film is squeezing through the developing rollers, a pod containing a developing solution is broken and the developing solution is spread over the exposed instant film. Thereby, a latent picture photographed on the instant film is developed to be a visible positive picture.
Because the sheet size of the instant film is relatively large, the instant camera must have a sufficiently large room for loading the instant film, so it is difficult to make the instant camera compact in comparison with 35 mm cameras and APS cameras using IX 240 type film. In order to improve the portability of the instant camera, JPA 4-194829 discloses a collapsible instant camera wherein a lens board having a taking lens therein is mounted to a camera body through bellows so that the board may be folded onto a front wall of the camera body or protruded from the front wall. Because the collapsible instant camera is complicated in construction and needs a large number of parts, the production cost is high and the collapsible instant camera comes to be expensive.
It is desirable to introduce such a lens barrel in the instant camera that has been used in conventional compact cameras and is movable between a stowed position and at least a protruded position, but there are many problems to solve in practice. It is necessary to provide a second motor for driving the lens barrel besides the motor for the film feed out mechanism, since the movable lens barrel is driven by a motor in one direction to protrude or in a second or opposite direction to retract. In addition, where the taking lens is focused through a focusing mechanism that is driven by a different motor from that used for protrusion and retraction of the lens barrel, the instant camera must mount at least three motors. This is disadvantageous in view of compactness and cost.
To reduce the number of motors, JPZ 1869801 discloses a teaching to use rotational power of a motor in one direction for moving a lens barrel between a wide-angle position and a telephoto position, and rotational power in the other or opposite direction for driving another mechanism, e.g. a film advancing mechanism or a shutter charging mechanism. Also, JPA 9-236854 discloses a teaching to drive a film advancing, winding and rewinding mechanism by rotating a motor in one direction and drive another mechanism by rotating the motor in the other direction.
However, these prior arts just propose the teaching, and do not disclose any concrete solution for the achievement. For instance, there is no teaching how to move the lens barrel in opposite directions by rotating the motor in one direction, or how to focus the taking lens. Moreover, the torque necessary for driving one mechanism is usually different from that for another mechanism. When using the rotational power of the same motor for different mechanisms, the difference in the torque must be taken into consideration. Otherwise, the mechanism cannot operate stably and would rise a certain noise.
Meanwhile, many of instant cameras and inexpensive cameras use a taking lens with a relatively short focal length and a relatively small lens aperture, so that the taking lens covers a wider subject distance range within the depth of field. In those instant cameras or inexpensive cameras, the whole subject distance to cover is often divided into several zones, e.g. near, middle and far distance zones, and the taking lens is designed to be set to one of several focusing positions determined for the respective subject distance zones. It is well-known in the art to provide a manually operated zone focusing device instead of or in addition to an automatic focusing device. The zone focusing device allows the photographer to designate one of predetermined subject distance zones so as to focus the taking lens on the designated subject distance zone.
In the conventional zone focusing device, an operation member, such as a switching lever or dial, is connected to a focusing ring of the taking lens through an interconnection mechanism to switch over the focusing position by rotating the focusing ring through the operation member. So the operation member has been located in proximity to the taking lens to improve the space efficiency and simplify the interconnection mechanism. However, the conventional location of the operation member of the zone focusing device is not handy for the photographer, and also limit the layout of other camera elements.
In view of the foregoing, an object of the present invention is to provide a camera, wherein a lens barrel of a taking lens can move back and forth along an optical axis by rotating a motor in one direction.
A further object of the present invention is to provide a camera, wherein rotational power of a motor in one direction is used for focusing as well as for moving a lens barrel back and forth.
Another object of the present invention is to provide a camera which uses rotational power of a motor in one direction for driving a lens barrel mechanism, and rotational power of the motor in the other direction for driving another mechanism, while considering differences in necessary torque between these mechanisms.
Still another object of the present invention is to provide a camera with a manually operated zone focusing device wherein an operation member of the zone focusing device may be located in an appropriate position without lowering the space efficiency of the camera.
According to the present invention, a camera is comprised of a barrel driving assembly immovable in the direction of an optical axis of the taking lens and including a drive ring, the drive ring being rotated about the optical axis in one direction when a rotational power of a motor in a first direction is transmitted to the drive ring; a movable barrel assembly holding a taking lens therein, and movable back and forth along the optical axis of the taking lens relative to the camera body; and a cam mechanism interconnecting the barrel driving assembly and the movable barrel assembly such that the movable barrel assembly makes at least one stroke of reciprocative movement along the optical axis while the drive ring makes one revolution in the one rotational direction.
According to this configuration, it is possible to use a rotational power of the motor in a second direction for driving a second mechanism, such as a film feed out mechanism for an instant film unit or a film advancing mechanism for a roll film. Therefore, it is unnecessary to provide a separate motor for the second mechanism.
By interconnecting the drive ring with the motor through a clutch mechanism that is switched over according to rotational direction of the motor, the rotational power of the motor in the first direction is transmitted to the drive ring, and a rotational power of the motor in the second direction to the second mechanism.
According to a preferred embodiment, a motor drive device of the camera supplies a different amount of electric power per unit time to the motor for rotating the motor in the first direction from that supplied for rotating the motor in the second direction, in accordance with differences in necessary rotational power between the drive ring and the second mechanism.
According to a preferred embodiment, the movable barrel assembly comprises a movable barrel, and the barrel driving assembly comprises the drive ring, whereas the cam mechanism comprises an endless cam groove provided on one of the movable barrel and the drive ring and at least a cam pin provided on the other of the movable barrel and the drive ring. The cam pin is engaged in the endless cam groove through an axial guide slit formed through an axial guide member, and the endless cam groove has segments extending obliquely to the rotational direction of the drive ring such that the cam pin moves back and forth in the direction of the optical axis at least once while the drive ring makes one revolution in the one rotational direction.
By providing the endless cam groove with at least two front segments that extend in a circumferential direction and are shifted in the direction of the optical axis from each other, the movable barrel may be stepwise set to at least two different protruded positions by rotating the drive ring in the one direction. By making the taking lens be set at different focusing positions at the different protruded positions of the movable barrel, it is unnecessary to provide a separate focusing motor beside the motor used for protrusion and retraction of the movable lens barrel.
According to another preferred embodiment, the movable barrel assembly comprises a rear movable barrel movable back and forth along the optical axis relative to the camera body while rotating about the optical axis, and a front movable barrel holding the taking lens and mounted in the rear movable barrel so as to be movable back and forth along the optical axis relative to the rear movable barrel, whereas the cam mechanism comprises a first cam mechanism interconnecting the rear movable barrel with the barrel driving assembly such that the rear movable barrel rotates together with the drive ring in the one rotational direction and makes at least one stroke of reciprocative movement along the optical axis per one revolution, and a second cam mechanism interconnecting the rear movable barrel and the front movable barrel such that the front movable barrel makes at least one stroke of reciprocative movement along the optical axis while the rear movable barrel makes one revolution.
A first endless cam groove of the first cam mechanism and a second endless cam groove of the second cam mechanism have similar contours to each other, and cam pins of these cam mechanisms move along the endless cam grooves simultaneously in the same direction by the same angular amount. By providing least one of the first and second endless cam grooves with at least two front segments that extend in a circumferential direction and are shifted in the direction of the optical axis from each other, the front movable barrel may be stepwise set to at least two different protruded positions relative to the camera body by rotating the drive ring in the one direction.
Also in this case, it is preferable to determine the different protruded positions of the front movable barrel in correspondence with different focusing positions of the taking lens, in order to use the motor for protrusion and retraction of the movable lens barrel and for focusing as well.
According to a preferred embodiment, the camera further comprises a zone focusing device having a manually operated zone selecting member for selecting a subject distance zone to be focused on by the taking lens from among different subject distance zones. The zone focusing device generates a zone selection signal representative of the subject distance zone selected through the zone selecting member. By determining the different focusing positions of the taking lens in correspondence with the different subject distance zones, it is possible to set the taking lens at one of the different protruded positions by controlling the motor in accordance with the zone selection signal. Because the focusing of the taking lens is carried out responsive to the zone selection signal, the manually operated zone selecting member may be located at an appropriate position on the camera body. Since it is unnecessary to provide an interconnecting mechanism between the taking lens and the zone selecting member, the space efficiency of the camera is improved.